The present invention relates to a multichannel/multicircuit communication control unit or controller, and in particular, to a multichannel/multicircuit communication controller suitable for communications employing an integrated services digital network (ISDN).
With an increase in communication speed and with a growth of the capacity of data to be communicated, the contents of communication control has been changed in information processing apparatuses such as a personal computer and a workstation. Namely, as a result of the increased load imposed on the communication control, it has been difficult in such an information processing apparatus for a system processor dedicately achieving information processing to conduct the data transmission control while supervising a line controller. To cope with this difficulty, there has been proposed a method in which a line controller and a processor exclusively achieving a communication control processing are disposed in a communication adapter so as to minimize the communication control load imposed on a system processor. The communication adapter is implemented in an extension board to be connected to a system bus. The method above has been described, for example, in the JP-A-63-292656.
However, when the method is adopted to control a plurality of communication lines or channels, a communication adapter is required to be installed for each line or channel. That is, a plurality of extension boards are to be connected to the system bus. This results in an increase in the size of the apparatus; furthermore, it is necessary for the system processor to respectively control the plural adapters disposed in the respective extension boards. Moreover, there arises a difficulty in the information exchange between communication processors disposed in the respective communication adapter boards. Particularly, for example, in the ISDN, since a line is multiplexed to accommodate three channels including two B channels and one D channel (2B+D) and the D channel functions to achieve a call control for the B channels, it is difficult for three adapter boards to handle the respective channels 2B+D.
Because the communication line speed is stipulated to be constant in the ISDN, there also occurs a difficulty to conduct communications via the ISDN with conventional terminals operating at various communication speeds.